Closed mercury manometer



Feb. 16, 1954 H HESSE 2,669,125

` CLOSED MERCURY MANOMETER Filed Sept. 9, 1952 Patented Feb. 16, 1954 l -UNITED .STATES PATENT OFFICE oLosEb MERCURY MANOME'TER Holger Hesse, Vedbwek, Denmark Application september 9, 1952, serial No. '308,539

51 Claims. (Cl. I3-402) The present invention relates to mercury manometers, particularly sphygm'omanometers.

Conventional sphygmomanorneters comprise a manometer, a rubber cuit and an inating ball with a release valve; the mancmeter may be a spring manometer or a mercury manometer, the latter usually being employed for the reason that the absence of resilient members, e. g. springs, in their construction ensures longevity and freedom from calibration errors arising out of variations in vthe properties oi said resilient memn bers. However., mercury manometers are necessarily bulky, and vsince sphygmomanometers have usually to be portable, the indication zone of the manometers are usually restricted to permit indication of pressure only up to about 270 mm. Hg, although it is occasionally desirable to be able to read pressures up to about 30G mm. I-g.

Conventional sphyg-mcmanometers are thus usually furnished with an open mercury manometer having a tube length of at least 270 mm.; in order to obtain a more compact apparatus it has been proposed to employ closed mercury manometers, the manometer tube being closed at its upper end to provide a compression space for gas trapped above the mercury column, the pressure of such gas supplementing the hydrostatic pressure due to the mercury column. Thus, by suitable dimensioning of the said compression space, the mancmeter tube may be made as short as desired, e. g. so that a mercury column of about 100 mm. height may indicate a pressure of 300 mm. Hg.

However, such a closed manometer must be vented immediately prior to use in order to bring the pressure in the compression space to the pressure of the surrounding atmosphere, since the pressure in the compression space otherwise may vary in an uncontrollable way, for example, owing to temperature changes; it is known, therefore, to provide the compression space with a push-button venting valve for actuation prior to use of the apparatus.

This known construction is unsatisfactory in that on the one hand actuation of the venting valve is liable to be forgotten and on the other hand, the valve may become leaky in time owing to wear or deposition of dust in its mechanism, whereby considerable incalculable measuring errors may arise.

In accordance with the present invention, there is provided a closed mercury manometer, having a branch conduit in communication with the manometer tube above the zero level of the mercury therein and below the compression ,2 space, such branch conduit being closed by a 'plug which' is permeable to air but impermeable 'to mercury. By this construction it will be appreciated that, at, zero pressure, the compression space in the manometer tube is always vented, and that the mercury rising under pressure in the manometer tube above the -level `of' the branch conduit automatically seals rsaid conduit. The said plug may comprise a ceramicmass or a leather disc.

The invention will be explained by reference to some embodiments shown by way 'ci Iexample in the accompanying drawings, in which- Figure 1 is a front elevation, partly in section of a sphygmomanometer constructed lin accordance with one embodiment of the invention; g

Figure 2 is a front elevation of another :embodiment; y

Figure 3 is a perspective view of 'a 'further embodiment; and

Figure 4 is a section on an enlarged scale through the manometer tube.

Referring to Figure 1, reference numeral "I designates a socket for connecting the appa ratus to a source of air under pressure, said socket leading to a container 2 for mercury 3'.

The container 2 is connected to a manometer tube 5 by means `of a `conduit Ail. The socket 'I is provided with a leather disc (not shown) which is permeable to air but not to mercury. The manometer tube 5 pression space I I.

A branch conduit 'l2 extends from manomete'r tube 5 at a point somewhat above the zero level of 'the mercury therein, the branch conduit l"l2 conveniently comprising a tube closed by a plu-g in the form Vof a porous leather disc i3 which is trapped between two blocks 'lil and I5. 'The blocks I4 and 'I5 are connected with each other by means of screws i6. lOne of the blocks I-' is provided with a bore I8 permitting air to flow from the leather disc i3 to the atmosphere, whilst the other block l5 is provided with an inspection bore I'l through which the mercury zero level may be observed. As long as atmospheric pressure prevails at the socket I, the space I I is connected to atmosphere via tube 5, leather disc I3 and bore I8 so that the initial pressure in space Il always is atmospheric irrespective of temperature changes which may have occurred since prior use of the apparatus. When blood pressure measurements are made, air under pressure is supplied via the socket I to the mercury container 2 with the result that the mercury column rises in the manometer tube 5 is connected with a com- 3 and the branch conduit I2 is automatically sealed from the latter. The mercury will continue to rise in manometer tube 5 until the sum of the hydrostatic pressure of mercury and of the compression pressure in tube 5 and space II balances the pressure applied to socket I. The measured values are read on a scale 8 extending along tube 5. As the measurement only takes a short time, temperature changes in the atmosphere will not aiect the readings taken.

In the embodiment shown in Figure 2, the branch conduit is connected to the manometer tube at the same point as in the embodiment prising a porous disc I3 or the like located inv an internally threaded housing 28 and held in position by means of an externally threaded sleeve 29.

This construction has several advantages in that the inspection bore I1 oi the embodiment shown in Figure 1 is eliminated and the plug may be arranged in any convenient position externally of the manometer tube; `there is also a further advantage in that the column of mercury rising in the riser conduit 25 fills the latter when the mercury is only about one third up the scale e. g.; thus the lower third of the scale is compressed with respect to the upper two thirds and thus offsets'the compression of the upper part of the scale which results from the eiect of the compression space I I. Thus the scale is substantially uniform.

In order to prevent a mercury plug, formed by turning the manometer tube to a horizontal position, e. g. during transport, from being retained in the tube 5 by reduced pressure in the compression space and not returning to the mercury container when the manometer tube is restored to a vertical position, a split concentric tube 26 of synthetic resin or similar resilient material is preferably inserted into the manometer tube 5 as shown in Figure 4. This tube effects the dissipation of any mercury plug formed.

In the embodiment shown in lFigure 3, the manometer is housed in a spool on which the rubber cuff may be wound. Thus the manometer shown in Figure 1 is disposed within a cylindrical container I9 which is provided with top and bot tom ilanges 20, 2|. After use, the cui may be wrapped around the container I9 between the ilanges 20 and 2I and the space occupied by the apparatus thereby minimised. As in the embodiment shown in Figure 1, the manometer tube is designated 5, the scale 8, the branch conduitsupporting block I5, and the inspection bore I1. A hose socket 22 is provided for connecting the 4, manometer to the mercury container and the cuff.

WhatIclaim is:

1. A manometer comprising a measuring tube portion, a means containing mercury connected to one end of said portion and adapted to receive a pressure to be measured for moving mercury into said tube portion in an amount corresponding to the magnitude of said pressure, a branch conduit connected to said tube portion and communicating with the ambientatmospliere, said tube portion being otherwise closed off, and a gas-permeable plug closing said conduit, said plug being impermeable to mercury and said tube portion being iilled with gas over the mercury, whereby the gas pressure in said tube portion will be in equilibrium with atmospheric pressure Whenever the level of mercury does not cut oi communication between the tube portion and the branch conduit.

2. A manometer according to claim 1 wherein the plug is an air-permeable animal membrane.

3. A manometer according to claim i wherein the plug comprises ceramic material.

4. A manometer according to claim 1 wherein said branch conduit carries two blocks, one supporting said plug and the other being furnished with an inspection bore for viewing the zero level of the mercury in the measuring tube. I

5. A manometer according to claim 1 wherein said branch conduit comprises a riser conduit closed at its upper end by a gas-permeable plug which is impermeable to mercury.

6. A manometer according to claim 1 wherein a split resilient tube is disposed coaxially within the measuring tube to form a liner therein for dissipation of any mercury plug formed in the measuring tube when it is in a horizontal position and retained in the measuring tube and not returning to the means containing mercury when the measuring tube is restored to a vertical position.

7. A manometer according to claim 1 wherein the manometer is housed in a cylindrical con-,1

tainer having upper and lower iianges to form a spool about which a rubber cuff receiving the pressure to be measured may be wrapped when not in use.

HOLGER IPIESSE,v l

References cited in the fue of this patent UNITED STATES PATENTS 

